In order to increase the power output of an internal combustion engine of a particular displacement volume, additional air can be supplied by compressing the air by means of a turbocharger. Additional air permits the burning of more fuel to produce increased power output.
At very low engine speed such as, for example, at low idle, there is insufficient exhaust gas energy to drive the turbocharger fast enough to produce significant levels of boost. Consequently, there is an appreciable lag time between opening of the engine throttle and when the turbocharger is running fast enough to produce enough boost pressure to eliminate smoke on acceleration. Fuel control devices, such as rack limiters or aneroid controls, are employed to limit the amount of fuel delivered to the engine cylinders until the turbocharger is capable of delivering sufficient air to produce smoke-free combustion. These fuel limiting devices cause slower response to throttle opening and a sluggishness in engine and vehicle response.
There is need for boosting the output of an exhaust gas-driven turbocharger during those times when an increase in engine output power is required.